Scroll type positive displacement apparatus have attracted a great deal of interest for any of a variety of reasons including theoretical simplicity and, when used as a compressor or pump, the ability to generate very high pressures with an apparatus that physically is quite small, and the fact that they lend themselves to multi-stage configurations.
As is well known, scroll type apparatus are generally comprised of a pair of flat plates in generally parallel relation with each plate having one or more spiral vanes extending axially towards the other plate to interfit with vanes thereon. Depending upon the design, both plates may be rotated with one additionally orbiting with respect to the other or one plate may be merely orbited with respect to the other which is stationary. In either event, closed pockets defined by points of contact of the vanes travel between radially inner and radially outer locations at the interface between the plates and serve to convey fluid between ports disposed at such locations.
When used as a compressor or a pump, the radially outer port will be an inlet port while the radially inner port, frequently formed in a shaft supporting one of the scrolls, is an outlet port. As fluid is conveyed from the inlet to the outlet, the pressure is increased and such an increase in pressure tends to drive the plates axially apart. Should the plates move appreciably apart in the axial direction, the ability to seal the pockets is lost as is the efficiency of operation of the apparatus.
Consequently, the prior art has proposed preloading the plates towards each other in the axial direction. However, when it is desired to start up the preloaded apparatus, the large frictional forces existing at the points of contact between the scrolls make the apparatus hard to start.
To avoid these difficulties, the prior art has proposed the application of the outlet pressure to the side of either or both of the scrolls opposite the interface so that as pressure builds up at the interface during operation of the apparatus, which pressure tends to axially separate the plates, such pressure is also applied on the opposite side of the plate to counter balance the separating pressure.
This approach, while successful, has heretofore lent itself to scroll apparatus of the type where one scroll merely orbits with respect to the other and is not known to be used in those type of scroll apparatus wherein the scrolls both rotate with one scroll additionally orbiting with respect to the other. Furthermore, this approach necessitates the formation of a chamber on the side of at least one scroll remote from the interface which accordingly increases the bulk and axial length of the apparatus.
An example of this approach is illustrated in U.S. Pat. No. 4,384,831, issued May 24, 1983 to Ikegawa et al.
The present invention is directed to overcoming one or more of the above problems.